Conspiracy

The original plan of the Conspirators was that when they left, Fredegar (who had never left the Shire) was to stay behind to deal with any "inquisitive folk" and to keep up the pretense that Frodo was still living there by wearing Frodo's clothes and keeping about the place. After learning about the Black Riders, Fatty was invited to flee with the others into the Old Forest. He claimed to be too terrified of the stories of the Forest and instead voluntarily remained behind as a decoy for the Nazgûl and expect Gandalf in case he showed up, and tell him of the events. Though Merry tried to persuade Fatty that the Old Forest would be nothing compared to meeting the Ringwraiths, Fatty was adamant, so the other Hobbits went into the Forest.[3]

The Ringwraiths did eventually come in the night to Crickhollow for Frodo and the Ring, but Fatty, though frightened nearly witless, escaped to raise the alarm of Buckland. This caused the Nazgûl to flee, but they had learned that the Ring was gone.[4]

Resistance

During Saruman's rule of the Shire, Fatty led a group of partisans fighting against the Ruffians around the hills of Scary before eventually being captured. He was imprisoned in the Lockholes and starved, (and could no longer be called "Fatty") but was rescued after the victory of the Battle of Bywater.[1]

Etymology

Other versions of the Legendarium

In The Return of the Shadow, Fatty Bolger is said to have played a much larger role, but this was later abandoned. His role survives as a minor anomaly in the published The Lord of the Rings - before the Hobbits go into the Old Forest, they have five ponies prepared - but only take four. Fatty was originally supposed to go with them.